The overall objective of this project is the elucidation of the secretory process of gland cells in its major phases: I. Construction of the secretory granules containing the exportable products. II. Neurotransmitter control of secretion. III. The actual process of secretion. Our recent work on this project using rat parotid gland preparations has established three receptors for neurotransmitters in the control of the secretory process. Activation of Beta-adrenergic receptors initiates protein secretion while activation of alpha- adrenergic receptors and, independently, cholinergic receptors, initiate K ion release which is most probably associated with water secretion. Since all three receptors are apparently located within the same cell membrane it is planned to study their action at the level of the isolated cell membrane. The latter will also serve in attempts to cause fusion with the secretory granules in cell-free preparations. The properties of the secretory granule membrane and content components will be studied in order to understand their function in the granule construction. Methods: Isolation of purified cell membranes, secretory granules, and membrane vesicles, use of ionophores to study the function of Ca ions, quantitative electronmicroscopy.